Flexible tubes currently used for dispensing pastes do not generally have a dispensing valve. However it is very advantageous to provide such a valve, particularly if special valves known as precompression metering pumps are used. A particularly advantageous improvement of such valves is described in French patent number 2 305 241 (1975) enabling them to operate in any orientation relative to the vertical. One example of such an improved prior art pump is shown in various different positions in FIGS. 1 to 3.
Each of these figures is in vertical section and shows six different parts. Three of these parts are fixed relative to one another namely: a crimping cup 1 for sealing the valve assembly 10 to the neck of a paste-containing receptacle (not shown) in sealed manner; a turret 2 for placing on the outside of the receptacle; and a body 3 whose bottom end is immersed in the support of paste. The other three parts are mounted to slide vertically within the body 3, and comprise: a hollow piston rod 5; a double-ended valve member 4; and a return spring 6. In FIG. 1, the parts are in a configuration which corresponds to the rest position with the valve closed. Without going into full detail of pump operation, it is recalled merely that depressing the piston rod 5 compresses fluid trapped in pump chamber 7. When the compression overcomes the opposition of the spring 6, the fluid opens a passage 8 and escapes. The various parts are then in the relative positions shown in FIG. 3 where the valve is shown open.
Such a valve gives three qualities to a tube of paste. As a pump it ensures that at least 95% of the substance contained in the tube can be dispensed in use. Its metering function is particularly advantageous for pharmaceutical substances, but may be advantageous in other applications as well. Finally, precompression is essential for safety reasons in some applications, and in any application it ensures clean operation. The pressure that must be reached inside the chamber 7 so as to open the passage 8 is much higher than the pressure which can be set up inside the tube by squeezing it by hand. This greatly reduces any danger of substance being dispensed accidentally.
However, the use of such precompression metering pumps for dispensing paste encounters a problem with priming. When the valve is crimped onto the tube of paste, its chamber 7 contains air. When the piston rod 5 is depressed for the first time, this air compresses. However, as a gas, the air cannot reach a sufficiently high pressure to escape via the passage 8. That is why the body 3 is normally provided with a short spline 9. The skirt of the valve member 4 can then be caused to lift slightly away from the inner cylinder, thereby opening a passage to allow the air to escape into the receptacle (see FIG. 2). Although this system is effective at priming the pump when the tube contains a liquid, it is ineffective when the tube contains a paste because of the viscosity of the paste, since the air expelled into the supply of paste tends to remain close to the chamber 7 in the form of a bubble. When the piston rod 5 and the valve member 4 move back up, the same air is sucked back into the pump chamber 7 instead of the paste, as desired. This means that it is practically impossible to prime the pump.
French patent application number 2 625 729 describes a tube provided with a precompression metering pump, but overcomes this drawback by means of a tube whose wall is semi-rigid and by ensuring that there is sufficient initial pressure inside the receptacle. However, this requires specially-shaped tubes or flasks to be used. From an economic point of view it is more advantageous to continue using flexible tubes, as is the common practice. The object of the present invention is therefore to solve the problem of priming pumps used for dispensing pastes from flexible tubes.
The invention is based on the idea of establishing a vacuum inside the paste-containing tube. Present methods for obtaining such a vacuum in receptacles that are to be closed by a dispensing valve are essentially designed to operate with rigid flasks. They include a step of placing the valve on the flask by means of a device which bears against the walls of the receptacle, thereby sealing off a chamber. Air can then be sucked out from the chamber and the valve put immediately into place and then crimped on. No method has been proposed for flexible tubes other than welding through the substance they contain. However, this method which is used for example to split up a bleach-containing cylinder sausage-like into individual sachets, cannot be performed in the presence of pastes containing fat or grease.